16/06/26 19:59:08 ERROR SparkContext: Error initializing SparkContext.
org.apache.spark.SparkException: A master URL must be set in your configuration
at org.apache.spark.SparkContext.<init>(SparkContext.scala:401)
at net.jgp.labs.spark.HelloSpark.main(HelloSpark.java:10)

It means that you forgot to specify where the master is by using. You can resolve this by using: setMaster("local").